Abstract
Introduction
Proper rotational alignment of the tibial component in total knee arthroplasty (TKA) could be achieved using several techniques. The self adjustment methodology allows the alignment of the tibial component under the femoral component after several flexion-extension movements. Our hypothesis was that this technique allowed a posterior tibial component alignment parallel to the femoral component posterior bicondylar axis. The aim of this study was to access this hypothesis using a post-operative CT-scan study.
Materials and Methods
This prospective CT-scan study involved 94 TKA. Theses TKA were divided in two groups: group1: 50 knees with a pre-operative genu varum deformity (mean HKA: 172.2°), operated using a medial parapatellar approach, and group 2: 44 knees with a preoperative valgus deformity (mean HKA: 188.7°), operated using a lateral parapatellar approach. Four measures were done on each post-operative CT-scan: angle between anatomical transepicondylar axis and femoral component posterior bicondylar axis (FCPCA), angle between FCPCA and tibial component marginal posterior axis, angle between tibial component marginal posterior axis and bony tibial plateau marginal posterior axis (BTPMPA), angle between transepicondylar axis and tibial component marginal posterior axis. Each measure was repeated, after one month by the same independent observer. Statistical evaluation used non-parametric Wilcoxon–Mann–Whitney test to compare each group of measures, and intraobserver reproducibility was assessed using ANOVA test, with an error rate of 5%.
Results
Intraobserver measurements were reproducible. Mean FCPCA was to 3,1° (SD:1,91) in group 1 and 4,7° (DS: 2,96) in group 2. Tibial component was positioned in external rotation in both groups, in relation to FCPCA: (group 1: mean angle: 0,7° (SD:4,45), group 2: mean angle: 0,9° (SD:4,53)) and in relation to BTPMPA: (group1: mean angle: 6,1° (SD: 5,85); group2: mean angle: 12,5° (SD: 8,6)). There was no statistical difference between these two groups.
Tibial component was positioned in internal rotation in relation to anatomical transepicondylar axis: (Group1: mean angle: 1,9° (SD: 4,93); group 2: mean angle: 3° (SD: 4.38))
Discussion
By using the self adjustment technique, tibial component is aligned parallel to the femoral component regardless of the initial frontal deformity and the surgical approach. However, there was a difference in tibial component axis and BTPMPA, between the two groups. This difference should be explained by the difference in morphology of the tibial plateau bone in knee with genu valgum deformity. The self adjustment technique is a reliable method to obtain a proper rotational alignment of the tibial component in TKA.
